Well, the JT Proteus features that made it good are no longer included in the current protues editions.
-Strap attaches at back of mask, and doesn't cover ears=That no longer exists.
-Now solid black instead of transparent smoke
These were many of the reasons that people wanted the proteus, and now with the current proteus' there is really nothing special about them. So I say save about 35.00 and buy a new Flex-7 IZE.
As far as getting a fan:
Does your current mask fog constantly? Ask yourself if it is really worth an extra 50.00. I wouldn't buy one unless you need it, it is quite pointless. If you do fog up constantly even with the thermal lenses this brings up a new issue............
The proteus comes with a fan so it is basically a 50.00 mask with a 50.00 fan. So buying the proteus "kit" would be cheaper than buying an IZE and upgrading to a fan. So if you need the fan, I suggest buying the proteus, cause you get more for your dollar.
With the proteus though you can't choose your color, so you have to think about that. The IZE offers 6 different colors and the Proteus only offers solid black.
I'm assuming that you like the looks of both masks, so what I said boils down to:
Need a fan=Proteus
Fan not neccessary=IZE
Hope that helps